This invention relates to the operation of combined cycle power plants, and more particularly, to an improved method of starting the power plant, using a variable loading rate strategy, to reduce emissions including visible emissions such as “yellow plume”.
In many locales, electrical utilities have power plants located close to urban areas. If the utility uses gas turbines for power generation, it is common for visible pollutants, commonly referred to as “yellow plume” to be emitted from exhaust stacks of the plant when the gas turbines are started. Yellow plume occurs when the amount of NO2 produced during start-up exceeds 20 parts per million or ppm. Yellow plume is a visible discharge from the exhaust stacks at the power plant and since the stacks are typically quite tall, the yellow plume is readily visible over a large area. The yellow plume condition is typically temporary only and the plume dissipates as the gas turbines in the plant reach their nominal operating status. However, it is common for the visible plume to last for upwards of an hour or more which can result in complaints from those in the area about the plant.
It has been found that by modifying the plant start-up procedure, the amount of time the NO2 exceeds 20 ppm is substantially reduced. This not only reduces the amount of time a yellow plume may be produced, but lowers the amount of these emissions produced during the start-up cycle.